Current wind turbine designs typically utilize direct drive generators or gear driven generators coupled to the wind turbine shaft. In such designs, there is an inherent problem in that as the wind speed varies the output frequency of the generator will also vary. However, for the generator output to be usable by the power grid, the output signal needs to be converted to match the power grid frequency, which is 60 Hz in the United States and 50 Hz in Europe. Typically, an additional frequency conversion stage is used to convert from the variable wind turbine generator output frequency to the constant grid frequency. Such an additional frequency conversion stage can include invertors and/or other phase correction circuitry. Such conversion stages can be costly and complex to implement and maintain. In addition, there is an inherent inefficiency which results in the frequency conversion process resulting in lost energy. It would be desirable if new methods and apparatus for wind turbine designs resulted in the generator output frequency being controlled to match the power grid frequency without the need for an additional frequency conversion stage.
Current wind turbines designs which connect to a power grid provide no or very limited warning of the loss of output due to unfavorable wind conditions. Loss of generator output can be due to low wind or no wind conditions resulting in insufficient wind energy to continue to drive the turbine. Loss of generator output can also be due to high wind conditions which could overstress the wind turbine elements if the wind turbine operation was allowed to continue, and thus the wind turbine is typically intentionally taken off-line during the interval of detected high winds to prevent damage to the wind turbine. Inconsistencies of the wind turbine generator output power level and rapid cutoffs result in balancing problems from the perspective of power grid management. Under such conditions, the power grid has a very small amount of time to locate and bring on line alterative sources of power to continue to balance the grid, regulate voltage levels within an acceptable band, prevent line voltage sags/spikes in order to continue to meet customer energy requirements and/or maintain an acceptable quality of service. It would be desirable if new methods and apparatus for wind turbine designs resulted in the wind turbine generator output being controlled to provide a more uniform power output level irrespective of changing wind conditions. It would also be beneficial if new methods and apparatus of wind turbine designs provided for more gradual degradations in energy output levels and/or provided earlier warnings to the power grid of an impending loss of output power.
Following a shutdown, current wind generator turbines typically need to use electricity/power from the grid to reinitialize themselves and get back in operation. In many cases, a low velocity wind does not provide enough energy to start the rotation of the wind turbine so power from the grid is needed to drive a motor to start the spinning. Wind turbine start-up energy requirements place additional loads on the power grid. In a grid coupled to a larger number of similar or identical wind turbines in the same general area subject to the approximately the same wind conditions, it would not be unusual for many of these wind generator turbines to try to start up at approximately the same time, thus placing a substantial short term additional load on the grid. In view of the above, it would be advantageous if the methods and apparatus were developed which allowed the wind turbine generates to start up under their own power, following an interruption due to wind conditions, thus removing the start-up loading burden placed on the grid, which draws energy from the grid and tends to upset grid power balancing management.
Another problem facing current wind turbines is that the energy absorption bandwidth is typically rather narrow. Most current wind turbines are shut down at wind velocities which are either too low or too high. A typical wind velocity bandwidth for existing wind turbine systems is approximately 9 mph to 25 mph. It would be beneficial if new methods and apparatus of wind turbine designs expanded the energy absorption bandwidth allowing the wind turbine to continue to absorb wind energy for lower and/or higher wind velocities than current systems, thus capturing more wind energy on average over time.
Current wind turbines have turbine blades, which are designed to produce energy in a 9 mph to 25 mph band. In order to produce energy in low velocity winds the blades can be variable pitch blades, which allow for the capture of energy at low wind speeds. In order to be able to catch the low velocity wind energy and operate the turbine, the turbine blade area has to be sufficiently large. However, implementing a large turbine blade area designed to accommodate the capture of wind energy at relatively low wind velocities becomes a detriment to the capture of wind energy at relatively high wind velocities, as the larger size blades increase the likelihood of potential structural failure at the high wind velocities. Therefore, with such an implementation using larger size turbine blades to capture energy from low velocity winds, the wind turbine is required to be shutdown at a lower upper wind velocity limit to prevent potential structural damage. In view of the above it would be advantageous if new methods of apparatus of wind turbine design are adaptive to accommodate the unique design requirements at both the low velocity end and high velocity end.
Current wind turbines have very limited or no energy storage capability. Intervals of high wind energy capture time due to favorable wind conditions within the energy absorption band typically do not correspond to customer power level requirements. The excess energy is typically either wasted, e.g., burned off by a power consuming activity of the wind turbine, or dumped into the grid with the grid power management adjusting energy input from another source, e.g., decreasing energy output at fossil fuel power plant, to accommodate for the increased energy from the wind source. Even small improvements in wind turbines can lead to significant energy efficiencies and corresponding environmental benefits. Accordingly, it would be advantageous if methods and apparatus of wind turbines were developed so that the wind turbines included significant energy storage capability. In addition, it would be highly desirable if the range of wind speeds at which turbines could be used to produce power could be increased.